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IC 


8943 



Bureau of Mines Information Circular/1983 




Interim Performance Specifications 
for Transducer Modules Used 
With the Bureau of Mines 
Intrinsically Safe Mine 
Monitoring System 

Carbon Monoxide, Methane, and Air Velocity 
By J. E. Chilton and A. F. Cohen 




UNITED STATES DEPARTMENT OF THE INTERIOR 




Information Circular 8943 

Interim Performance Specifications 
for Transducer Modules Used 
With the Bureau of Mines 
Intrinsically Safe Mine 
Monitoring System 

Carbon Monoxide, Methane, and Air Velocity 
By J. E. Chilton and A. F. Cohen 




UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 




-^^^ 



XX-^ q^ 






^o 



This publication has been cataloged as follows: 



Chilton, J. E 

Interim performance specifications for transducer modules used with 
the Bureau of Mines intrinsically safe mine monitoring system. 

(Information circular / United States Department of the Interior, Bu- 
reau of Mines ; 8943) * 

Bibliography: p. 20. 

Supt. of Docs, no.: I 28.27:8943. 

1. Mine safety— Equipment and supplies. 2. Transducers. 3. Mine 
gases— Measurement, 4. Air flow— Measurement. I. Cohen, A. F. II. Ti- 
tle. III. Series: Information circular (United States. Bureau of Mines) ; 
8943. 

-"ma^^rU^- 622s [622'.81 83-600165 



CONTENTS 

Page 

Abs tract 1 

Introduction 2 

Bureau of Mines fixed-point ISMMS 2 

Low-current transducer modules for the ISMMS 3 

Interim performance specifications for transducer modules 3 

Part 1 . — Carbon monoxide * 3 

General 3 

Commercially available carbon monoxide transducer modules 9 

Part 2 . — Methane 9 

General 9 

Commercially available methane transducer modules 13 

Part 3. — Air velocity 14 

General 14 

Commercially available air velocity transducer modules 18 

Summary and conclusions 19 

Carbon monoxide 19 

Methane 19 

Air velocity 20 

References 20 

ILLUSTRATION 

1 . Carbon monoxide transducer module 4 

TABLES 

1. Interim performance specifications for carbon monoxide transducer modules.. 5 

2. Manufacturers and properties of commercially available CO transducers 9 

3. Interim performance specifications for methane transducer modules 10 

4. Manufacturers and properties of commercially available methane transducers. 13 

5. Interim performance specifications for air velocity transducer modules 15 

6. Manufacturers and properties of commercially available air velocity 

transducers 18 





UNIT OF MEASUREMENT 


ABBREVIATIONS 


USED IN THIS REPORT 


A/s 


ampere per second 


mg/m^ 


milligram per cubic meter 


•c 


degree Celsius 


yA 


microampere 


ft 


foot 


ys 


microsecond 


ft/min 


foot per minute 


pet 


percent 


h 


hour 


pH 


potential of hydrogen 


kohm 


kllohm 


ppm 


part per million 


mA 


mllllampere 


psl 


pound per square Inch 


m/s 


meter per second 


s 


second 


mV 


millivolt 


V 


volt 



INTERIM PERFORMANCE SPECIFICATIONS FOR TRANSDUCER MODULES 
USED WITH THE BUREAU OF MINES INTRINSICALLY SAFE 
MINE MONITORING SYSTEM 

Carbon Monoxide, Methane, and Air Velocity 

By J. E. Chilton 1 and A. F. Cohen 2 



ABSTRACT 

Interim performance specifications are presented for carbon monoxide, 
methane, and air velocity transducers used in the Bureau of Mines in- 
trinsically safe mine monitoring system. These specifications give 
quantitative values or qualitative descriptions of the transducers , in- 
cluding environmental parameters and monitoring system measurement and 
maintenance requirements as recommended by the Bureau of Mines. Commer- 
cially available transducer modules and prototype modules are listed 
together with selected characteristics. 



^Research chemist. 
^Physicist. 
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 





INTRODUCTION 



The periodic preshift, onshift, and 
weekly inspections for hazardous condi- 
tions in coal mines required by the Code 
of Federal Regulations (9^)-^ include mea- 
surement by portable equipment of methane 
(CH4) and air velocity at the working 
face in idle workings, in each air split, 
and in the main air returns. Other than 
thermal fire detectors along beltways 
or machine-mounted methane monitors, 
no means of continuous monitoring is 
required. The continuous monitoring of 
the mine environment with methane, air 
velocity, and low-level carbon monoxide 
transducers could significantly improve 
mine safety and production through the 
early detection and correction of hazard- 
ous conditions (_5 , 8^) . 

To meet this need, the Bureau has de- 
signed and is testing a new type of sys- 
tem called the intrinsically safe mine 
monitoring system (ISMMS) (_5 ) . This sys- 
tem is computer operated for the display 
and reporting of gas concentrations and 
air velocity data, and the generation 
and display of alarms when selected 



thresholds for measured mine air param- 
eters are exceeded. The system consists 
of a surface-mounted computer, intrinsi- 
cally safe power supplies, surface- 
to-underground mine electrical cables, 
telemetry systems, and transducer mod- 
ules^ for each measured parameter. 

The ISMMS was designed so that the mon- 
itoring system would continue to operate 
in mine emergencies. This system mea- 
sures in-mine environmental conditions 
even if the mine is closed or sealed and 
mine power is shut off. Knowledge of the 
mine environment during an emergency 
could pinpoint the location of mine 
fires. This knowledge in turn will help 
speed mine recovery operations and in- 
crease the safety of miners engaged in 
rescue efforts. 

An experimental version of the ISMMS 
has been installed and is operating at 
the Safety Research Mine at the Pitts- 
burgh Research Center and in a commercial 
coal mine in Pennsylvania. 



BUREAU OF MINES FIXED-POINT ISMMS 



Power for the ISMMS is supplied above- 
ground by a separate commercial power- 
line, making it independent of mine 
power; in addition, the system has a 
limited-duration battery supply. The 
system includes a microprocessor control- 
ler to record and display data and 
generate alarms , used in conjunction 
with intrinsically safe transducer power 
supplies. The aboveground ISMMS sup- 
plies both intrinsically safe power 
and bidirectional communications to the 
underground transducers through an ap- 
proved four-conductor cable. Up to four 

^Underlined nvunbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



separate safe trunk circuits , each with 
an intrinsically safe power supply 
(ISPS), can be used in the system. Each 
intrinsically safe power supply provides 
up to 18 Vdc at 800 mA for operating the 
transducers. 

^A transducer module as referred to in 
this report is a device containing a sen- 
sor, an amplifier with voltage regulator, 
and a telemetry system which contains an 
analog-to-digital converter and a bidi- 
rectional data transmitter. A sensor is 
an electrical device that produces an 
electrical signal in response to a spe- 
cific parameter such as CO or CH4 concen- 
trations, air velocity, or temperature. 



LOW-CURRENT TRANSDUCER MODULES FOR THE ISMMS 



To accommodate at least 20 parallel- 
connected transducer modules on one in- 
trinsically safe trunk line for a typical 
mine subsection, a current of 40 mA per 
transducer module would be the upper 
limit. Of the 40 mA, approximately 6 to 
15 mA is required for a power regulator, 
a signal amplifier, and a Conspec ac- 
cessor. 5/6 Thus, the desired sensors 
should operate on less than 25 mA. 



requirement. Available methane sensors 
require at least 60 mA {2); for this rea- 
son, the search for lower current methane 
sensors and/or transducers is part of 
an ongoing Bureau effort. Commercial 
carbon monoxide transducers are avail- 
able that operate at currents as low 
as 8.5 mA, including the accessor, and 
thus amply fulfill the minimum current 
requirement . 



At least one type of air velocity 
sensor exists that meets this current 

INTERIM PERFORMANCE SPECIFICATIONS FOR TRANSDUCER MODULES 



Because there is presently no history 
of in-mine experience with the Bureau's 
ISMMS monitoring system, the performance 
specifications presented here are pre- 
liminary. Changes in these specifica- 
tions may be made depending on the re- 
sults of Bureau research projects on 
transducer properties and as system per- 
formance data are obtained in the mine 
tests. The initial values recommended 
for the transducer properties were lim- 
ited to those obtained by available 



commercial modules , and these values may 
not fulfill the ideal intrinsically safe 
transducer requirements. The ISMMS spec- 
ifications in this report meet all of the 
present performance requirements stated 
for portable monitors in 30 CFR (9^). 

In addition to performance specifica- 
tions, approximate costs have been in- 
cluded to aid the design engineer in as- 
sessing economic benefits of the ISMMS. 



PART 1. —CARBON MONOXIDE 



By J. E. Chilton 



GENERAL 

The intrinsically safe mine monitoring 
system placed restrictions on the proper- 
ties of the carbon monoxide transduc- 
er modules; these restrictions include 
low-current operation, low sensor cost, 
minimum interference from other gases , 

^A telemetry device that converts the 
analog output to digital signal for 
transmission to the computer at the 
surface. 

"Reference to specific products does 
not imply endorsement by the Bureau of 
Mines. 



and stable long-time response. Carbon 
monoxide detector methods that are used 
in commercially available sensors operate 
on four different principles: electro- 
chemical oxidation of CO, absorption of 
infrared energy, heat of combustion of CO 
in air on a solid catalyst (Hopcalite) , 
and change of electrical conductivity of 
solid state materials. The carbon monox- 
ide transducer that best meets the system 
restrictions uses an electrochemical sen- 
sor, and the interim performance speci- 
fications have been written specifically 



with this 
mind. 



sensor's characteristics in 



The interim performance specifications 
for the carbon monoxide transducer have 
been divided into four sections: system 
design requirements, measurement require- 
ments, environmental requirements, and 
maintenance and other requirements. 
These interim specifications (table 1) 
can be met by commercial carbon monox- 
ide sensors with conventional electronic 
an^)lifier designs. A diagram of the 
transducer module is shown in figure 1. 



on, drawing extra current, which may 
additionally limit the total number of 
transducers used per line. 

A displaced or live zero is recommended 
for use, e.g., if a zero gas signal value 
of 0.5 V is used then a 0.0 V-output 
would indicate a transducer failure mode. 
The range of to 50 ppm was recommended 
for the CO transducers so that CO could 
be used for early detection of fires. 



The transducer module for carbon monox- 
ide consists of a CO sensor with a sensi- 
tivity of 0.5 yA/ppm CO or greater to 
minimize the noise contribution. The 
sensor and amplifier yield a signal of up 
to 5 V output full scale. On-site (in- 
mine) calibration of the CO transducer 
can be performed using a Mine Safety and 
Health Administration (MSHA) approved 
digital voltmeter; the calibration will 
be simplified if the calibration signal 
is direct reading, e.g., a 50-mV signal 
for 50 ppm CO gas. The accessor shown in 
the figure uses 4.5 mA, and the amplifier 
current needs can be minimized by the use 
of newer solid state amplifier circuitry 
where possible. The current limits have 
been set to allow a maximum number of 
transducers on a single line. Some gas 
transducer designs have incorporated 
light-emitting diodes (LED's) for zero 
and span set points. The LED's need 5 to 
7 mA additional current to operate; if 
the mine atmosphere is normally 0.0 ppm 
CO, the zero signal LED will remain 



Other concentration ranges, to 
500 ppm CO, may be considered if monitor- 
ing for health or toxic gas environment 
is contemplated. The Mine Safety and 
Health Administration (MSHA) requirement 
for toxic levels of CO is 50 ppm CO for a 
time-weighted average miner exposure for 
an 8-h shift, with short-term exposure 
limits of 400 ppm CO. The overall accu- 
racy requirement was written to include 
response variations due to precision, 
linearity over range, calibration error, 
drift over 1-month duration, and tempera- 
ture changes of 10° C for a CO trans- 
ducer. The 2-min response time for the 
CO transducer is necessary because trans- 
port of CO to the sensor occurs by con- 
vection and diffusion alone, and these 
transport processes are slow. Pumped 
sampler sensors have faster response 
time, but they have not been considered 
because of the excessive current use of 
the electric pump motors. A faster re- 
sponse will reduce the time required 
to calibrate the transducer. 



0.5A^A/ppm CO 



Sample gas 
to 50 ppm CO 



Sensor 



0.5to4.5V 



Amplifier 



\ 

Accessor 



Power 

8 to 18 V 

less than 10 mA 

+ 



t t 
Calibration signal 

to 0.5V or to 5 V 

for to 50 ppm CO gas 

FIGURE 1. - Carbon monoxide transducer module. 



■I 



TABLE 1. - Interim performance specifications for carbon monoxide transducer modules 

(For Bureau of Mines remote underground continuous fixed-point intrinsically 
safe coal mine monitoring system) 



Characteristic 



Interim performance 
specifications 



Rationale 



1.0 SYSTEM DESIGN REQUIREMENTS 



1,1 Carbon monoxide 

transducer module 
input current , 
continuous . 



1.2 Transducer module 

current, surge upon 
power application. 

1.3 Transducer module 

input voltage. 



1.4 Electrical system 

and transducer mod- 
ule recovery time 
following loss of 
power to monitoring 
system. 



1.5 Output signal 

current. 

1 . 6 Output signal 

voltage. 



1.7 Output signal 
behavior. 



Current less than 10 mA. 



Current increase shall be lin- 
ear with resistive character 
without overshoot or surge. 

Normal operating voltage is 8 
to 18 Vdc and must withstand 
intrinsic safety tests at 
26 Vdc. 



Response will meet accuracy 
standards within 20 min. 



At least 1 mA at full output 
voltage, 5 V. 

0.5 to 4.5 V for zero to full- 
scale CO concentration 
(50 ppm) . V indicates mal- 
functioning or unpowered 
transducer. 

A monotonic signal with voltage 
value increasing for an in- 
crease of CO concentration. 



The BOM ISMMS power supply has a current 
limit of 800 mA per trunkline. The total 
number of CO-transducer modules that can 
be attached to 1 trunk line is determined 
by the individual transducer currents. 

The power supply will turn off if load ex- 
ceeds 800 mA or if sudden changes in 
voltage or load current are detected. 

The transducer module will be powered by 
the Bureau-designed power supply which 
operates at 18 Vdc and meets intrinsical- 
ly safe operation requirements (7^) . The 
voltage at a transducer depends on its 
distance along the cable and total number 
of transducers on a trunk line. 

All transducers exhibit a stabilization or 
warmup time after power turn on. Elec- 
trochemical-based CO transducers have 
been found to produce a full-scale output 
followed by a slow recovery to the normal 
response upon reapplication of power fol- 
lowing a power interrupt of several min- 
utes. During recovery the transducer is 
not responding accurately , and its output 
must be ignored. The recovery period 
should be kept short to minimize the loss 
of the monitoring ability of the system. 

The accessor input impedance is 5 kohm. 



The accessor maximum input voltage is 5 V. 
Live zero (0.5 V for ppm CO) is neces- 
sary for detection of transducer 
malfunction. 



A single-valued signal is necessary for 
unambiguous interpretation of data. 



2.0 MEASUREMENT REQUIREMENTS 



The range shall be to 50 ppm 
CO or higher. 



2.1 CO measurement 
range. 



The range is limited to low values of con- 
centration to conform with MSHA early 
fire warning protocol (6), which speci- 
fies that alarms are to be set for 5 ppm 
and 10 ppm above normal CO background. 
Accessor resolution is 1 in 256 for 5 V. 
Full-scale (4.5 V and 50 ppm) gives 
0.2 ppm digital resolution. 



TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued 



Characteristic 



Interim performance 
specifications 



Rationale 



2.0 MEASUREMENT REQUIREMENTS— Continued 



2.2 Overall accuracy, 



2.3 Response-rise time.. 



2.4 Response-recovery 
time. 



2.5 Response upon ap- 

plication of pow- 
er after power 
inter rupt-reco very 
time. 

2.6 Stability-zero, re- 

sponse variation 
with time in pure 
air. 



2.7 Stability-span, re- 
sponse variation in 
sensitivity with 
time. 



2.8 Calibration: 

2.8.1 Procedure. 



2.8.2 Calibration — 
test gas. 



The response to CO concentra- 
tion within the transducer 
module range for a 1-month 
period shall have an inaccu- 
racy including bias and pre- 
cision of less than ±2 ppm CO 
at a sample concentration of 
5 ppm CO or less and ±4 ppm 
CO at a sample concentration 
of 25 ppm CO. 

Upon applying a step increase 
in CO concentration to a 
transducer module, the time 
interval from initial response 
to a response value that is 
90 pet of final value shall be 
less than 2 niin. 



Upon applying a step decrease 
in CO concentration to a 
transducer module, the time 
interval from initial response 
to a response value 10 pet 
greater than the final value 
shall be less than 2 min. 

Same as 1.4. Response shall 
meet accuracy specification in 
less than 20 min from applica- 
tion of power. 



The response drift in pure air 
shall be less than ±1 ppm CO 
per month. 



The response drift (change in 
sensitivity) with a CO chal- 
lenge gas shall be ±10 pet of 
the gas concentration per 
month or less. 



A standard calibration proce- 
dure must be specified by 
transducer manufacturer for 
in-mlne calibration. 

A calibration kit shall contain 
necessary parts for test and 
reset (if necessary) of zero 
and span setting at the mine 
by means of the measured 
transducer responses. The 
test gases shall have an anal- 
ysis accuracy of ±1 pet or 
less of stated reading. 



Accuracy shall include response variation 
terms from calibration error, precision, 
drift, and temperature changes (_1^) . 

See rationale of 2.1. False alarms from 
response inaccuracy must be minimized. 



CO transducer modules have response times 
of 2 min or less. Fast transducer re- 
sponse is recommended for mines with CO 
sources such as diesel haulage to dis- 
criminate between short- and long-term 
CO concentration changes to aid fire de- 
tection. Fast response will decrease 
the time required to calibrate the 
transducers. 

See rationale 2.3. 



Same as rationale for 1.4. 



Response variation with time for unad- 
justed continuous operation with no CO 
present should be much less than MSHA- 
recommended alert level for monthly cali- 
bration schedule (6^) . 

The response variation in transducer out- 
put from drift in presence of CO should 
be less than total accuracy requirement, 
and calibration should be needed no more 
frequently than once per month to main- 
tain accuracy. 

Uniform procedure for calibration shall be 
used to maintain transducer accuracy for 
intercomparison of measured values within 
mine. 

Accuracy of transducer must be checked and 
transducer reset on-site using standard 
calibration gases. 



TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued 



Characteristic 



Interim performance 
specifications 



Rationale 



2.0 MEASUREMENT REQUIREMENTS — Continued 



2.8.3 Calibration 
duration. 



2.8.4 Calibration 

period. 

2.8.5 Calibration 

accuracy . 



Time for calibration and reset 
shall be less than 10 min. 



The period between calibrations 
shall be no more than 30 days. 

Response must be set to within 
overall accuracy by transducer 
calibration procedure. 



Minimize labor and time spent on calibra- 
tion operations and off-line time for 
transducers. Calibration time is deter- 
mined by transducer response time to zero 
and span gases, plus the attachment of 
fixtures, handling gas bottles, and 
adjustments. 

See rationale 2.8.3. 



Minimize bias between responses obtained 
with calibration kit and responses to 
equal concentrations of CO in mine. 



3.0 ENVIRONMENTAL REQUIREMENTS 



3.1 Intrinsic safety. 



3.2 Operating 

temperature. 

3.3 Storage temperature, 



3.4 Operating relative 
humidity. 



3.5 Atmospheric 
pressure. 



3.6 Corrosive 

environment. 



3.7 Shock, test, 



3.8 Electromagnetic in- 
terference (EMI). 



3.9 Sand, dust, and 
airflow. 



Transducer module must be de- 
signed and fabricated to meet 
requirements of MSHA Approval 
and Certification Center for 
operations in methane-air mix- 
tures, 30 CFR 18, Electric 
Mine Accessories (9). 

The transducer shall operate 
from 4° to 40° C within accu- 
racy requirements. 

The transducer shall tolerate 
storage from -40° to 50° C 
temperatures. 

Transducer shall meet accuracy 
requirements in atmospheres 
from 10 to 95 pet relative 
humidity. 

Transducer module operation 
will meet accuracy require- 
ments with pressure variations 
encountered in mines. 

Operation demonstrated after 
acid spray test (salt spray, 
if justified) pH 3.1 to 3.3, 
120 h. 

Survive drop test at 36-in 
height onto wooden floor. 

Survive conductive radiative 
susceptibility tests at mine 
radio communication frequen- 
cies and random power 
transients. 

Transducer shall operate in 
sand or dust to 10 mg/m^ and 
air velocity to 20,000 ft/min. 



Mine monitoring system must continue to 
operate in returns and throughout the 
mine in emergencies. 



Operational temperature limits are set by 
freezing point of sensor electrolyte and 
range of mine temperatures. 

Surface storage and transportation of 
transducer module or parts may be in un- 
controlled environments . 

Continuous operation in wet or dry mines 
will occur and must not cause failure of 
transducer electronic circuits or sensor 
or affect the accuracy of measurement. 

Ventilation and barometric pressure 
changes affect mine atmospheric pressures 
and may change CO transducer response. 



Continuous mine operation may result in 
contact with acid gases, dust, and liq- 
uids with air >95 pet relative humidity 
(3). 



Survive transport in mines; 
(4, 9). 



30 CFR 22.7 



Transducer interaction with EMI such as 
that from power transients or mine com- 
munications shall not cause false alarms , 



Transducer module operation and accuracy 
shall be minimumly affected by airflow or 
particulate deposition (3). 



TABLE 1. - Interim performance specifications for carbon monoxide transducer modules — Continued 



Characteristic 



Interim performance 
specifications 



Rationale 







3.0 ENVIRONMENTAL REQUIREMENTS— Continued 


3.10 


Physical properties: 
Size 


Minimum size. 

Have no sharp projections or 

corners . 
Make minimum weight. 
Mount in designated position. 


Safe and easy transportation and set up by 
miner; design for minimum dust and water 
drop interaction in upright position. 




Shape 

Weight 

Mounting 


3.11 


Specificity to car- 
bon monoxide. 


Effect on transducer response 
by other gases in mines shall 
be minimized. 


Gases such as methane or hydrogen sulfide 
naturally occurring in mines, nitrogen 
oxides from explosive fumes or diesel ex- 
haust, or hydrogen from battery charge 
stations shall cause minimum transducer 
response. 



4.0 MAINTENANCE AND OTHER REQUIREMENTS 



4.1 Field inspection and 

maintenance. 

4.2 Transducer parts 

replacement . 



4.3 Documentation. 



Minimum or no more frequently 
than calibration. 

Module replacement in mine; 
sensor life 1 year minimum. 

An operational and maintenance 
manual shall be supplied con- 
taining, as a minimum, the 
following items : 

Manufacturer's name, loca- 
tion, telephone. 

Unpacking and assembly 
procedures . 

Warranty information. 

Use restrictions. 

Intrinsic safety statements , 
agency, permit number, 
date. 

Principle of operation and 
theory. 

Operating instructions and 
detailed figures. 

Performance specifications. 

Calibration procedures , kit 
information, gas cylinder 
replacement. 

Gas Interference table. 

Maintenance instructions, 
circuit diagrams , trouble- 
shooting steps, voltage 
check points. 

Parts list, production num- 
ber of part, source, re- 
placement cost. 



Minimize maintenance costs (labor) , 



Minimize transducer out-of -service time, 



Adequate documentation is necessary for 
optimum transducer use and upkeep. 



i 



TABLE 2. - Manufacturers and properties of commercially available CO 
transducers (Manufacturer's specifications) 



Manufacturer 


Input 


Input 


Output 


Range, 






Estimated 


and model 


voltage, 
Vdc 


current , 
mAl 


voltage, 
Vdc 


ppm CO 


Drift 


Accuracy 


cost 1983 


Dynamation, 


5 -35 


3 


0.0-0.5 


0-500 


ND 


ND 


$500 


series 4000. 
















Energetics Sci- 


8 -28 


2l7 


-1 


0- 50 


ND 


ND 


$500 


ence, model 5001. 




324 




or 
0-500 








General Electric, 


7.2-30 


4 


.5-4.5 


0- 50 


(Zero) 


+1 ppm at 


ND 


model 15ECS6C01. 










± 1 ppm/ mo 


10 ppm CO 




InterScan, model 


±3 


2 


- .01 


0- 50 


ND 


±2 pet of 


$400 


114-D. 


or +15 




or 

- .20 


or 
0-250 




reading 




Mine Safety 


11 -28 


7.3 


.5-4.5 


0- 50 


ND 


ND 


ND 


Appliances . 

















ND No data. ^Current for transducer without accessor, 

^Current without ALARM function. ^With calibration LED on. 



The requirement of specific response to 
carbon monoxide may be relaxed if the CO 
transducer is used as an early fire- 
warning system. Fires in coal will pro- 
duce other oxidizable species such as 
nitrogen oxides , and these gases , in ad- 
dition to CO, will give an increased 
transducer response. If a mine has al- 
ternate sources of these gases, such as 
nitrogen oxides and carbon monoxide from 
diesel exhaust products, then a sensor 
specific to CO may be necessary, 

COMMERCIALLY AVAILABLE CARBON MONOXIDE 
TRANSDUCER MODULES 

The CO transducer modules are commer- 
cially available from a number of manu- 
facturers as either prototype devices or 
as a fully manufactured and MSHA- 
certified product. These manufacturers 
and selected CO transducer module proper- 
ties are summarized in table 2. The 



properties listed include input voltage 
and current, output voltage, range and 
drift, accuracy, and cost when the data 
were given. Although there are many more 
manufacturers of CO sensors and of port- 
able CO monitoring equipment, only those 
manufacturers known to produce transducer 
modules have been included in this list. 

Performance tests of some of the CO 
transducer modules have been conducted at 
the Bureau. These modules include proto- 
type units from General Electric (model 
15ECS6C01), Energetics Science (model 
5001), and Mine Safety Appliances. The 
CO performance specifications can, in 
general, be met by these transducer mod- 
ules. Five of the General Electric CO 
transducers have been installed in a co- 
operating coal mine in Pennsylvania and 
for the Past 11 months have received zero 
drift and periodic calibration check 
tests. 



PART 2. —METHANE 
By A. F. Cohen 



GENERAL 



The methane transducer module must be 
compatible with practical monitoring sys- 
tem needs of maximizing the number of 
modules per trunk line. The ideal ISMMS 
requirement of 40 mA for the transducer 
module (based on at least 20 transducers 



on a trunk line) cannot be realized with 
existing methane sensors; accordingly an 
interim operating current methane trans- 
ducer specification of 80 mA is given in 
table 3. This table lists methane trans- 
ducer characteristics, interim perform- 
ance specifications, and rationale. 



10 



TABLE 3. - Interim performance specifications for methane transducer modules 

(For Bureau of Mines remote underground continuous fixed-point intrinsically 

safe coal mine monitoring system) 



Transducer module 
characteristic 



Interim performance 
specifications 



Rationale 



1.1 Methane transducer 

module input current 
(continuous) . 



1.2 Transducer module 

input current (surge 
upon initial power 
application) . 



1 . 3 Transducer module 
input voltage. 



1.4 Electrical system and 
transducer module 
recovery time fol- 
lowing loss of power 
to monitoring system. 



1.5 Transducer output 

current. 

1.6 Transducer output 

voltage. 



1.7 Transducer output 
signal. 



1.0 SYSTEM DESIGN REQUIREMENTS 



Current less than 80 mA (1982 de- 
sign limits). 



Current increase shall be linear 
with time; circuit should be re- 
sistive looking (ohmic) and capa- 
ble of accepting a 500-vis turn-on 
without overshoot or surges in 
current. 

Normal operating voltage range is 
8 to 18 Vdc. Circuit must be 
capable of operating at 26 Vdc 
for intrinsic safety testing. 

Response will meet accuracy re- 
quirements within 20 mln. 

Also, same characteristic as (1.2) 
upon recovery. 



to 1 mA. 



0- to 5-Vdc range of detection; 
voltage to accessor should have i 
linear range from 0.25 to 5.0 V 
with dynamic range being 0.5 to 
4.5 V and output being 0.5 V at 
pet CH4 and 4.5 V at 5 pet CH4 , 
V indicates malfunctioning or 
unpowered transducer. 

Linear signal proportional to 
methane concentration in range 
of detection. 



Bureau of Mines ISMMS power 
supply has a current limit of 
800 mA per trunk line. The 
total number of methane trans- 
ducer modules on a trunk line 
is equal to the sum of the in- 
dividual transducer currents. 

Power supply current limiter 
will trip if current spike 
greater than 1 A/s is 
detected. 



The transducer module will be 
powered by the Bureau of Mines 
ISPS, which has a dynamic 
range of 8 to 18 Vdc. 

30 CFR 75.307 (9^). Limit time 
transducer module is out of 
service (to correspond to max- 
imum time of 20 min allowed 
between readings at the face 
in present CFR regulation for 
handheld instruments). 

Input impedance of accessor 
board is 5,000 ohms. 

Accessor input voltage requires 
5 V for maximum resolution 
with displaced zero. 



Linear requirement convenient 
for simple microcomputer 
usage. 



11 



TABLE 3. - Interim performance specifications for methane transducer modules — Continued 



Transducer module 
characteristic 



Interim performance 
specifications 



Rationale 



2.0 MEASUREMENT REQUIREMENTS 



2 . 1 Range 

2.2 Accuracy over a 30-day 

period in-mine, in- 
cluding factors that 
can affect accuracy; 
i.e., zero drift per 
month, span drift per 
month; poisoning by 
silicones or other 
vapors, zero shift 
and/or sensitivity 
changes due to momen- 
tary exposures of 
1.5 pet CH4 , or expo- 
sures to atmospheres 
with velocities of 
to 1,700 ft/min. 



2.3 Speed of response, 



2.4 Calibration: 

2.4.1 Procedure. 



2.4.2 Calibration kit. 

2.4.3 Ease of 

calibration. 



2.5 Specificity. 



to 5 pet methane in air 

Allowable variations in scale 
reading over 1 month are — 



Methane 


Minimum 


Maximum 


content , 


indication. 


indication. 


pet 


pet 


pet 


0.25 


0.10 


0.40 


.50 


.35 


.65 


1.00 


.80 


1.20 


2.00 


1.80 


2.20 


3.00 


2.70 


3.30 


4.00 


3.70 


4.30 



Accuracy must be maintained when 
exposed to range of air veloci- 
ties found in U.S. coal mines (0 
to 1,700 ft/min). 

Less than 60 s to reach 90 pet of 
final reading (for a step change 
in concentration) . 

A standard procedure should be 
specified by the manufacturer. 

A calibration kit shall be 
available. 

Calibration requires <15 min by a 
qualified person. 



In presence of other combustible 
gases , output signal should be in 
fail-safe direction; sensor 
should not be unduly affected by 
CO, CO2 , or water vapor. 



30 CFR 22.7 (9^). 

(a) Accuracy of portable meth- 
ane detectors and (b) sensor 
is calibrated and zeroed on 
monthly schedule. 

Calibration once per month. 
Measured CH4 concentrations 
(due to all factors) must not 
differ from true values (for 1 
month operating time) by more 
than allowed in table given 
here. 



Typical range of air velocities 
in U.S. coal mines extends 
from to 1,700 ft/min. In 
most mines it is 200 to 600 
ft/min. 

Achievable by transducer module 
manufacturers . 



A uniform procedure is avail- 
able to maintain accuracy. 



Downtime of system minimized. 

30 CFR 75.307 (9^). "Monitor 
for Methane at 20-Min Inter- 
vals During the Operation of 
Electrically Operated Equip- 
ment" requirement. 

Coal mines may contain other 
combustible gases (hydrogen, 
ethane) . Sensor should be 
made as specific as possible 
for methane. In presence of 
hydrogen or ethane , the net 
signal will be greater than 
for methane alone (in fail- 
safe direction) . 



3.0 ENVIRONMENTAL REQUIREMENTS 



3.1 Intrinsic safety. 

3.2 Ambient storage 

temperatures . 



3.3 Relative humidity. 



Must meet MSHA approval for in- 
trinsic safety. 

Must be operational between -20° 
and +40° C within accuracy re- 
quirements; must survive storage 
temperatures between -40° C and 
+50° C. 

Operational at 30 to 100 pet rela- 
tive humidity (coal mines). 



30 CFR 27 (9^). 

Representative underground tem- 
peratures in U.S. coal mines 
(3). 



Dayton T. Brown, Inc. (3). 



12 



TABLE 3. - Interim performance specifications for methane transducer modules — Continued 



Transducer module 
characteristic 



Interim performance 
specifications 



Rationale 



3.0 ENVIRONMENTAL REQUIREMENTS—Contlnued 



3.4 


Atmospheric pressure 


Calibratable and operational be- 


Dayton T. Brown, Inc. (3). 




(equivalent) . 


tween 9.7 and 19.7 psi. 
Low pressure equivalent to 10,000 

ft above sea level. 
High pressure equivalent to 10,000 

ft below sea level. 




3.5 


Corrosive environment. 


Functional after acidified salt 
spray test (5 pet salt; pH 3.1 to 
3.3). 


Do. 


3.6 


Shock 


Must survive drop test at maximum 
height (36 in) onto a wooden 


Do. 












floor. 




3.7 


Electromagnetic 


Must survive all conducted and ra- 


Do. 




interference. 


diated susceptibility tests using 
National Bureau of Standards 
spectral densities without trans- 
ducer degradation. 




3.8 


Sand and dus t 


Must be operational at 10 mg/m-' 


30 CFR 27.22 (9). 






dust up to 1,750 ft/min (air 








cleaner test dust classified from 








Arizona Road Dust). 




3.9 


Size, shape, and 


Minimum weight and size consistent 


Physical damage in close quar- 




weight. 


with sufficient ruggedness to en- 


ters possible. To insure sys- 






dure mine environment. 


tem reliability, easy install- 
ation of transducer module, 
and easy maintenance, minimum 
size and weight are required. 


3.10 


Design and 


Must be able to be hung or sup- 


30 CFR 75.308 - 75.310 (9). 




restrictions. 


ported in mine in appropriate 
places to monitor adequately. 
Must survive normal mine 
operations. 





4.0 MAINTENANCE AND OTHER REQUIREMENTS 



4.1 Maintenance: 

(a) Inspection. 



(b) Parts replacement. 

(c) Parts availability 

4.2 Sensor life 

4.3 Documentation, instal- 

lation, and user's 
manual. 



Performance inspection no more 
frequent than once per week un- 
less sensor is clearly inopera- 
tive (fault condition). 

Inspection: Check span drift and 
accuracy at 2.5 pet CH4 ; check 
drift at zero gas. If total 
drift (zero drift and span drift) 
out of specification (see accu- 
racy), recalibrate. Labor and 
material for inspection less than 
1 pet of unit transducer cost. 

Less than 1/2 h by qualified main- 
tenance personnel. 

Spare parts must be available. 

>1 year. 

Manufacturer should provide clear 
and complete installation and 
user's manual and troubleshooter 
guide, including detailed circuit 
diagrams and calibration proce- 
dure for mine use. 



Cost consideration. 



Do. 

Accuracy requirement and to in- 
sure system reliability. 



13 



To insure the intrinsic safety of the 
system, the transducer modules must be 
intrinsically safe. Response time must 
be sufficiently short (<60 s) and recov- 
ery time of the transducer under loss 
of power must be sufficiently short 
(<20 min) for continuous monitoring in- 
tegrity. Accuracy must be maintained 
between monthly calibrations. Finally, 
the transducer module must survive the 
coal mine environment and meet practical 
tests such as physical size and weight. 

Section 1.0 of table 3 refers to sys- 
tems requirements specific to the ISMMS 
for continuous fixed point operation. 
Section 2.0 concerns methane measurement. 
Individual characteristics include items 
related to accuracy of methane detectors 
as stipulated in 30 CFR 22.7 ( 9^) . If we 
assume a monthly calibration schedule, 
the maximum methane transducer total 
drift and effects on transducer output 
such as poisoning, lack of specificity, 
high-concentration methane bursts, and 
air velocity level, taken together, must 
be such that the permitted deviation in 
accuracy (30 CFR 22) is not exceeded over 
a monthly operating period. Response 



time, maintenance, and range of detection 
are included in the table. For the pres- 
ent, the transducer range is limited to 
0- to 5-pct CH4 concentrations. 

The intrinsic safety specification 
(3.1) is used to satisfy the permissibil- 
ity requirement (30 CFR 27) (9^). 

Items 3.2 to 3.8 are environmental fac- 
tors, such as temperature and pressure, 
which the transducer must be able to 
endure. 

COMMERCIALLY AVAILABLE METHANE 
TRANSDUCER MODULES 

As has been stated, the components of 
the first iteration of the ISMMS other 
than the intrinsically safe power supply 
were to be as nearly as possible off- 
the-shelf (commercially available) items. 
Table 4 lists commercially available 
methane transducer modules and character- 
istics essential for use in the ISMMS. 
In addition to current and voltage 
characteristics, range of detection and 
cost, if available, are given. 



TABLE 4. - Manufacturers and properties of commercially 


available methane transducers 




Input 


Input 


Output 


Range of 


Cost 


Manufacturer and model 


voltage. 


current , 


voltage. 


detection. 


(1982) 




Vdc 


mA 


Vdc 


pet CH4 




J&S Sieger, Ltd. (England) BMl 


10.7 -16.0 


ND 


0.4-2.0 


0.0-3.0 


ND 


detector head (00747-A-OOOl) 












with English Electric Valve Ltd. 


I2.O 


II8O 








sensor VQZ. 












MSA mine surveillance methane- 


13.0 -15.0 


700 


ND 


.0-5.0 


Approx. 


sensing assembly (built for BOM) 










$800 per 


with MSA series 510 sensor 










channel 


463163. 


I1.88 


I4OO 








J-Tec Associates model VMlOl with 


10.5 -18.0 


140 


.0-5.0 


.0-5.0 


<$1,000 


English Electric Valve Ltd. sen- 












sor VQl. 


I2.2 


I375 








J-Tec Associates model VMIOIB 


12.0 -21.0 


75 


.5-5.0 


.0-5.0 


$950 


with Scott Aviation sensor: 












Standard, 40008560 


I5.5 


l60 








Prototype, 40010161 


I5.5 


l60 








Texas Analytical Controls Inc. 


7.0 - 8.0 


75-80 


.2-3.0 


.0-3.0 


$300 


combustible gas sensor assembly 












(part 200A) with Scott Aviation 


I5.5 


l60 








standard sensor 40008560. 













Nd No data. Censor only. 



14 



It should be noted that manufacturers 
of the many available portable or fixed 
instruments that measure methane concen- 
tration are potential providers of trans- 
ducers. However, instrument manufactur- 
ers who do not provide CH4 transducers 
have not been listed here. 

Two transducer modules using the 60-mA 
Scott Aviation sensor are available 
(table 4, last two items). The last man- 
ufacturer has only recently been produc- 
ing this module, which has not yet been 
tested, and laboratory tests to date at 
the Bureau have been limited to model 
VMIOIB methane transducer modules by 
J-Tec Associates. Results for the sen- 
sor in this module (particularly Scott 
sensor part No. 40010161) appear good (2^) 
for ISMMS use. The commercially avail- 
able methane transducer module (J-Tec 
No. VMIOIB using sensor No. 40010161) has 



a response time of <30 s and a 0- to 5- 
pct CH4 range and is expected to satisfy 
the accuracy requirement between monthly 
calibrations. An initial sensor burn-in 
period (for the sensor) may be required. 

Thorough laboratory testing of many 
table 3 characteristics using six J-Tec 
methane transducer modules with the stan- 
dard 40008560 sensor is in progress at 
the Pittsburgh Research Center. J-Tec 
VMIOIB modules with the standard sensors 
have been installed at the Bruceton Safe- 
ty Research Coal Mine for in-mine tests, 
as well as at a cooperating coal mine in 
Pennsylvania. 

Further research is indicated to reduce 
the transducer current required by at 
least a factor of to meet perceived 
methane-sensing requirements for under- 
ground coal mines using ISMMS. 



PART 3. —AIR VELOCITY 



By A. F. Cohen 



GENERAL 

The ideal ISMMS requirements for air 
velocity transducers would include capa- 
bility of generating an output at very 
low velocities (<10 ft/min) and yielding 
information on directions of flow in case 
of airflow reversal. To date, no one air 
velocity transducer meets all require- 
ments. Therefore, the interim velocity 
transducer specifications do not include 
direction of the air velocity nor mea- 
surement of velocities below 50 ft/min. 

Table 5 lists transducer characteris- 
tics, interim performance specifications, 
and rationale. Section 1.0 relates to 
specifics of the ISMMS mine monitoring 
system. The low current (item 1.1) and 
18-Vdc limitation (item 1.3) are associ- 
ated with the Bureau's ISPS design char- 
acteristics; item 1.2 relates to the 
presence of a current limiter. 

Section 2.0 of table 5 is con- 
cerned with air velocity measurement 
and with environmental and operational 



requirements necessary to obtain maximum 
information and operating life. 

Transducer characteristics include 
items related to accuracy (item 2.2). 
Assuming a monthly calibration schedule, 
the total of factors that may affect the 
air velocity transducer accuracy such as 
total drift, temperature, or pressure 
change must not exceed the allowed devia- 
tion of air velocity over a monthly in- 
mine operating period. 

Table 5, section 2,0, includes response 
times appropriate to real mine condi- 
tions and calibration of transducers. 
For the present, consideration is limited 
to coal mines, hence, mostly to 200- to 
600-ft/min air velocities. The intrinsic 
safety specification is used to satisfy 
the permissibility requirement (30 CFR 
27). Also included are environmental 
factors such as temperature, pressure, 
dust, and humidity, which the transducer 
must be able to endure. Other items for 
practical consideration are size, weight, 
design restrictions, cost, and lifetime. 



15 



TABLE 5. - Interim performance specifications for air velocity transducer modules 

(For Bureau of Mines remote underground continuous fixed-point intrinsically 

safe coal mine monitoring system) 



Transducer module 
characteristic 



Interim performance 
specifications 



Rationale 



1 .0 SYSTEM DESIGN REQUIREMENTS 



1.1 Air velocity module 
input current 
(continuous) . 



1.2 Transducer module in- 
put current (surge 
upon initial power 
application) . 



1.3 Transducer module in- 
put voltage. 



1.4 Electrical system and 
transducer module re- 
covery time following 
loss of power to mon- 
itoring system. 



1 . 5 Transducer output 

current. 

1.6 Transducer output 

voltage. 



1.7 Transducer output 
signal. 



Current less than 40 mA. 



Current increase should be linear 
with time; circuit should be re- 
sistive looking (ohmic) and capa- 
ble of accepting 500-ys turn-on 
without overshoot or surges in 
current. 

Normal operating voltage range is 
8 to 18 Vdc. Circuit must be ca- 
pable of operating at 26 Vdc for 
intrinsic safety testing. 

Response will meet accuracy re- 
quirements within 20 min. 

Also, same characteristic as (1.2) 
upon recovery. 



to 1 mA. 



0- to 5.0 
tection; 
to 0- to 
min velo 
to acces 
range of 
ic range 
being 0. 
4.5 V at 



-Vdc active range of de- 
0.5 to 4.5 V corresponds 
1,000 or 0- to 3,000 ft/ 

city transducer. Voltage 

sor should have linear 
0.5 to 5.0 V with dynam- 
of 0.5 to 4.5 V, output 

5 V at zero velocity and 
maximum velocity. 



Linear signal proportional to air 
velocity in range of detection. 



Bureau of Mines ISMMS power 
supply has current limit of 
800 mA per trunk line. Total 
number of air velocity trans- 
ducer modules on each trunk 
line is equal to the sum of 
the individual transducer 
currents. 

Power supply current limlter 
will trip if current spike 
greater than 1 A/s is 
detected. 



Transducer module will be pow- 
ered by Bureau power supply, 
which has dynamic range of 8 
to 18 Vdc. 

30 CFR 75.307 (9^). Limit time 
transducer module is out of 
service (to correspond to max- 
imum time of 20 min allowed 
between readings at the face 
in present CFR regulations for 
handheld instruments). 

Input impedance of accessor 
board is 5,000 ohms. 

Accessor input voltage requires 
5 V for maximum resolution 
with displaced zero. 



Linear requirement convenient 
for simple microcomputer 
usage. 



2.0 MEASUREMENT REQUIREMENTS 



2 . 1 Range . 



2 models should be available: 50 
to 1,000 ft/min (0.25 to 5.0 m/s ) 
(most applications) and 50 to 
3,000 ft/min (0.25 to 15.0 m/s). 
(Transducer must respond to ve- 
locity of 50 ft/min at low end.) 



30 CFR 75.301-4 (9^). Minimum 
mean entry air velocity must 
be 60 ft/min. 

Typical range of air velocities 
in U.S. coal mines is to 
1,700 ft/min. In most coal 
mines it is 200 to 600 ft/min. 



16 



TABLE 5. - Interim performance specifications for air velocity transducer modules — Continued 



Transducer module 
characteristic 



Interim performance 
specif ica t i ons 



Rationale 



2.0 MEASUREMENT REQUIREMENTS— Continued 



2.2 Accuracy (over a 30- 


±10 pet of reading >150 ft/min.... 


Sensor calibrated and zeroed on 


day period) of air 




monthly schedule. 


velocity in-mine in- 






cluding those factors 


±20 pet of reading in range 50 to 


30 CFR 75.301-4 (9) . Minimum 


that can affect accu- 


130 ft/min. 


mean entry velocity at face = 


racy such as zero 




60 ft/min. 


drift, span drift, 






temperature, and 




According to ventilation engi- 


pressure. 




neers, ±10 pet of reading is 
desirable accuracy for 150- to 
1,000 ft/min air velocity. 

Typical range of air velocities 
in U.S. coal mines extends 
from to 1,700 ft/min. In 
most coal mines it is 200 to 
600 ft/min. 




Absolute accuracy of device must 


Factors to be considered for 




be within ±10 pet of true value 


in-mine calibrations are being 




after installation and in-mine 


determined. 




calibration at 150 to 1,000 ft/ 






min ±20 pet of true value at 50 






to 140 ft/min. 




2.3 Speed of response 


<120 s to reach 90 pet of final 
reading (for a step change in 
velocity) . 




2.4 Calibration: 






2.4.1 Procedure 


A standard procedure should be 


A uniform procedure is avail- 




specified by the manufacturer. 


able to maintain transducer 
accuracy for intercomparison 
of measured values with mines. 


2.4.2 Calibration kit.. 


A calibration kit or equivalent 


Accuracy of transducer to be 




should be available for in-mine 


checked without system upset 




calibration, for zero reset if 


or alarm. 




required, and for cleaning trans- 






ducer if required (dust). 




2.4.3 Ease of calibra- 


Calibration requires less than 


Minimize time for calibration 


tion and cali- 


15 min by a qualified person. 


and off-line time for 


bration 




transducers. 


schedule. 


Velocity transducer to be cali- 
brated every 30 days. 





3.0 ENVIRONMENTAL REQUIREMENTS 



3. 


1 


Intrinsic safety 


Transducer module must meet re- 
quirements for intrinsic safety. 


30 


CFR 27 i9). 


3. 


2 


Ambient and/or storage 
temperatures. 


Must be operational between -20° 
and +40° C within accuracy re- 
quirements; must sustain storage 
temperatures between -40° and 
+50° C. 


Representative U.S. underground 
coal mine temperatures. 

Dayton T. Brown, Inc. (3^). 


3 


3 


Relative humidity 


Operational at 30 to 100 pet rel- 
ative humidity. 




Do. 


3 


.4 


Atmospheric pressure 
(equivalent) . 


Operational between 9.7 and 19.7 
psi. 

Low pressure equivalent to 
10,000 ft above sea level. High 
pressure equivalent to 10,000 ft 
below sea level. 




Do. 



17 



TABLE 5. - Interim performance specifications for air velocity transducer modules — Continued 



Transducer module 
characteristic 



Interim performance 
specifications 



Rationale 



3.0 ENVIRONMENTAL REQUIREMENTS—Continued 



3.5 


Corrosion. ............ 


Functional after acidified salt 
spray test (5 pet salt; pH, 3.1 


Dayton T. Brown, Inc. (3). 










to 3.3 for 120 h) . 




3.6 


Shock 


Must survive drop test at maximum 
height (36 in) onto a wooden 


Do. 












floor. 




3.7 


Electromagnetic 


Must survive all conducted and ra- 


Do. 




interference. 


diated susceptibility tests using 
National Bureau of Standards 
spectral densities without trans- 
ducer degradation. 




3.8 


Sand and dust. ........ 


Transducer must be operational at 
10 mg/m^ dust at velocities up to 


30 CFR 27.2 (9). 












1,750 ft/min (air cleaner test 








dust classified from Arizona Road 








Dust). 




3.9 


Size, shape, and 


Minimum weight and size consistent 


Physical damage in close quar- 




weight . 


with sufficient ruggedness to en- 


ters possible. To insure sys- 






dure mine environment. 


tem reliability, easy instal- 
lation of transducer module, 
and easy maintenance, minimum 
size and weight are required. 


3.10 


Design and 


Must be able to be hung or sup- 


Preferred placement of trans- 




restrictions. 


ported in mine in appropriate 


ducer at given site is cur- 






places to monitor adequately. 


rently under investigation. 






Must survive normal mine 








operations. 











4.0 MAINTENANCE AND OTHER REQUIREMENTS 


4.1 


Maintenance: 
(a) Inspection. 




Performance inspection no more 
than once per 2 weeks, unless 
sensor is clearly inoperative 
(fault condition). 

Inspection: Check accuracy at ex- 
isting air velocity. If out of 
calibration by >10 pet, recali- 
brate. Labor and material for 
inspection >1 pet of unit cost. 


Industry requires low mainte- 
nance cost. 

See accuracy (item 2.2). 


H 


(b) Parts replacement. 


<l/2 h by authorized maintenance 
personnel. 




B 


(c) Parts availability 


Spare parts kits must be available 
at the mine. 




4.2 


Sensor life. . . 




>3 years. 

Clearly written and complete in- 
stallation and user's manual 
should be provided by manufactur- 
er, including detailed circuit 
diagrams , and calibration proce- 
dures for mine use. 


CoQt" prtn^l Hpfa t" "1 on * 


4.3 


Documentation, instal- 
lation, and user's 
manual . 


Accuracy requirement and to in- 
sure system reliability. 



18 



To sum up, the air velocity transducer 
module must be compatible with the inter- 
im monitoring system, e.g., <40 mA (for 
20 modules per trunk line) and voltage 
input of 8 to 18 Vdc. In addition, to 
insure the intrinsic safety of the moni- 
toring system, system components such as 
the transducer modules must be intrinsi- 
cally safe. Response time of the trans- 
ducer must be less than 120 s to reach a 
90-pct final value. Transducer recovery 
time under loss of power must be short 
enough (<20 min) to maintain continuous 
monitoring integrity. Accuracy must be 
maintained over a monthly schedule. Ad- 
ditionally, the module must survive real- 
istic coal mine environments and meet 
practical needs such as small physical 
size and weight. 

COMMERCIALLY AVAILABLE AIR VELOCITY 
TRANSDUCER MODULES 

As noted, the components of the first 
iteration of the ISMMS, other than the 



ISPS, were to be as nearly as possible 
off-the-shelf (commercially available) 
items , including the air velocity trans- 
ducer modules. Table 6 lists commercial- 
ly available air velocity transducer mod- 
ules and characteristics essential for 
use in the ISMMS. In addition to voltage 
and current characteristics, range of de- 
tection, accuracy, and cost are given. 
Only a few types of commercially avail- 
able air velocity transducers are avail- 
able; a much larger number of air- 
velocity-measuring instruments (portable 
or fixed type) exist. Manufacturers of 
air velocity instruments are potential 
transducer suppliers. 

As can be seen in table 6, the J-Tec 
VA216B is the only transducer module with 
sufficiently low current (35 mA) to be 
considered for the ISMMS; the Thermosys- 
tems. Inc., transducer, which is next, 
requires more than three times higher 
current. 



TABLE 6. - Manufacturers and properties of commercially available 
air velocity transducers 



Manufacturer 


Input 


Input 


Output 


Range, 






and model 


voltage, 
Vdc 


current , 
mA 


voltage , 
Vdc 


ft/min 


Accuracy 


Cost (1982) 


J-Tec Associ- 


12-21 


35 


0-5 


50-3,000 


±2 pet of full 


$1,475 


ates, Inc., 




(maximum) 


(output 


or 


scale. 




VA216B-air 






linear) . 


50-1,500 




Replacement 


draft sensor. 






* 


(50-1,000 
available 
on order) . 




draft sen- 
sor (not 
contain- 
ment or 
circuit 
board) : 
$895 


Thermosystems , 


9 


120 at 


0-5 


0- 600 


±0.5 pet of 


$600 


Inc. , veloc- 




300 ft/ 


(output 




full scale 




ity trans- 




min 


linear. 




for to 600 




ducer model 






to 600 




ft/min. 




1610. 






ft/min). 








Kurz , model 


12-15 


200 


0-5 


0- 300 


±2 pet of full 


$495 


430, air 






(nonlinear 


or 


scale between 




velocity 






with 


0-1,250 


-20° and +60° 


(replace- 


transducer. 






velocity) . 


or 
0-2,500 


C; ±5 pet at 
-55° to -20° 
C and +60° to 
+125° C. 


ment probe 
$250). 



19 



The J-Tec VA216B module operates down 
to velocities of approximately 50 ft/min 
and requires 35 mA for output of to 
5 V (corresponding to to 1,000 ft/min); 
its performance is independent of high 
humidity and dust, and it has no moving 
parts. An earlier model (VA214) of the 
J-Tec vortex-shedding transducer module 
was very mineworthy under operating 
mine conditions (_7 ) . The J-Tec VA216B 
was chosen for use in the first iteration 
of the ISMMS because of the low current 
required and because of its expected 



insensitivity^ to environmental factors 
such as temperature, humidity, and dust. 

Thorough testing of most table 5 char- 
acteristics using J-Tec VA216B air veloc- 
ity transducer modules is in progress 
at the Bureau's Safety Research Mine at 
the Bruceton Research Center and at a 
cooperating coal mine in Pennsylvania. 
These results will provide the basis for 
further refinement of performance speci- 
fications for air velocity transducer 
modules to be used in the ISMMS. 



SUMMARY AND CONCLUSIONS 



The interim performance specifications 
for carbon monoxide, methane, and air 
velocity transducers in the Bureau- 
developed ISMMS have been prepared 
and are summarized in the following 
paragraphs. 

CARBON MONOXIDE 

The more stringent transducer require- 
ments for ISMMS are as follows: 

1. The transducer operating voltage 
shall range from 8 to 18 Vdc at a current 
less than 10 mA. 

2. The transducer response drift in 
pure air shall be ±1 ppm CO equivalent 
per month or less. 

3. The overall accuracy characteristic 
is given by the specifications that over 
a 1-month period the response inaccuracy, 
as a combination of bias and precision, 
shall be less than ±2 ppm CO at a sample 
concentration of 5 ppm or less and that 
the inaccuracy shall be less than ±4 ppm 
CO at a sample concentration of 25 ppm 
CO. 

These requirements are considered nec- 
essary for the reliable measurement of CO 
in an underground coal mine where back- 
ground levels can range from 5 to 20 ppm 
CO. These specifications can be best met 
by the use of a transducer containing an 
electrochemical carbon monoxide sensor 
with the sample supplied in a diffusion 
mode. A test of the operation of several 



prototype carbon monoxide transducers 
has been started in a commercial coal 
mine. 

An assessment of these interim stan- 
dards will be made upon review of 
the data obtained. Future performance 
specifications will be used to de- 
fine the absolute minimum number of 
parameters that environmental monitoring 
transducers should meet to fulfill the 
requirements of a reliable and effective 
instrinsically safe mine monitoring 
system. 

METHANE 

An interim current specification of 
80 mA per methane transducer module is 
given for use with the ISMMS because the 
desired transducer (40 mA) is not avail- 
able at present. Two commercially avail- 
able transducer modules that meet the in- 
terim specification (<80 mA) both use the 
same sensor (Scott). Laboratory and in- 
mine testing of one of these modules 
(J-Tec VMIOIB with the standard sensor) 
is in progress. 

'The VA216B operates on the principle 
that vortices are formed in air passing 
around an object. The vortices formed 
per unit time downwind from a cylinder 
(the object) are counted. The rate of 
vortex formation is proportional to air 
speed. J-Tec uses an ultrasonic method 
to count the vortices. The frequency is 
proportional to air speed. 



20 



AIR VELOCITY 

The J-Tec VA216B meets the interim per- 
formance specification of 40 mA cur- 
rent per transducer module. In addition, 
this module is expected to withstand the 
mine environment, with little upkeep and 



without being calibrated more than once a 
month. The results of testing table 5 
characteristics in-mine, coupled with the 
ongoing research, will provide the basis 
for further refinement of air velocity 
transducer performance specifications for 
use with the ISMMS. 



REFERENCES 



1. American Society for Testing and 
Materials. Standard Specifications for 
Carbon Monoxide in the Atmosphere, D-11 
Committee, Sampling and Analysis of Atmo- 
spheres. Philadelphia, PA, 1978, 4 pp. 

2. Cohen, A. F. , and G, H. Schnaken- 
berg, Jr. Applicability and Capabilities 
of Commercially Available Methane Sensors 
for Fixed-Point Underground Intrinsically 
Safe Coal Mine Monitoring. PRC Internal 
Rept 4420, April 1983, 15 pp.; informa- 
tion available from authors at the Pitts- 
burgh Research Center, Bureau of Mines, 
Pittsburgh, PA. 

3. Dayton T. Brown, Inc. Environ- 
mental Test Criteria for the Acceptabil- 
ity of Mine Instrumentation (con- 
tract J0100040). BuMines OFR 1-82, 1982, 
135 pp; NTIS PB 82-146335. 

4. Fisher, T. J., and M. Uhler. Re- 
search to Develop an Intrinsically Safe 
Monitoring System for Coal Mines. 
Proceedings of the 5th WVU Conference on 
Coal Mine Elect rotechnology, July 30,. 
31, August 1, 1980 (contract J0100049). 
BuMines OFR 82-81, 1981, pp. 20-1 to 
20-10. 



5. Ketler, A, Mine Monitoring Can Aid 
Production and Cut Costs. Coal Age, 
V. 86, August 1981, p. 60. 

6. Miller, E. J., P. M. Turcic, and 
J. L. Banfield. Equivalency Tests of 
Fire Detection Systems for Underground 
Coal Mines Using Low Level Carbon Monox- 
ide Monitors. Proc. 2d Internat. Mine 
Ventilation Cong., Reno, NV, Nov. 4-8, 
1979. American Institute of Mining, 
Metallurgical, and Petroleum Engineers, 
Inc., New York, 1980, pp. 27-1 to 27-8. 

7. National Fire Protection Associa- 
tion. Intrinsically Safe Apparatus for 
Use in Division 1 Hazardous Locations. 
NFPA Bull. 493, 1978, 55 pp. 

8. Scott, L. W. Remote Monitoring of 
Air Quality in Underground Mines. Bu- 
Mines RI 8253, 1977, p. 3. 

9. U.S. Code of Federal Regulations. 
Title 30 — Mineral Resources; Chapter 1 — 
Mine Safety and Health Administration, 
Department of Labor; Subchapters A-P, 
Parts to 199. July 1, 1982, 688 pp. 



INT.-BU.OF MINES, PGH., PA. 27032 

















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